Actually, taken by itself this verse wouldn’t suggest the wrath of God at all: iniquity isn’t wrath (of God anyway), iniquity is injustice (literally un-equity). Whenever we sin, we are doing injustice to God (and especially to the action of God, Incarnate as the Son, by the grace of which action we exist and have capabilities to choose to do justice or injustice at all.) There Jesus is, up on the cross, being sinned against by all of us: murdering God. Which God, in several ways, willingly set up, with the Son being complicit with the Father in this action. (I mention key portions of Isaiah 53 in that doc, too.)
It’s other verses of Isaiah 53 that suggest God is wrathing against His Servant–or anyway that some kind of wrath is being leveled against the Servant, for which God has primary responsibility.
Isaiah 53:3-6, 10, 12; “He was despised and forsaken of men, a Man of sorrows, and acquainted with grief; and like one from whom men hide their faces, He was despised and we did not esteem Him. Surely our griefs He Himself bore, and our sorrows He carried; yet we ourselves esteemed Him stricken, smitten of God and afflicted. But He was pierced through for our transgressions, He was crushed for our iniquities; the chastening for our well-being was upon Him, and by His scourging we are healed. All of us like sheep have gone astray, each of us has turned to his own way; but the Lord has caused the iniquity of us all to fall upon Him. …] But the Lord was pleased to crush Him, putting Him to grief. …] Therefore (says the Lord) I will allot Him a portion with the great, and He will divide the loot with the strong; because He poured Himself out to death and was numbered with the transgressors; yet He Himself bore the sin of many, and interceded for the transgressors.”
I don’t think anyone can seriously deny from Isaiah that God has the primary active responsibility in what is happening to the suffering servant–even though I don’t think anyone can deny either, at least from other scriptural data, that we are complicit in the death of Christ as well. (This happens to be a theme of the subsequent chapter, 54, that the wife rejected by the Lord God, her husband, for killing Him, will be restored by God eventually. Interestingly, the Lord compares this restoration of the universal Jerusalem–though Jerusalem isn’t mentioned by name–to God’s resolution after the flood of Noah never to flood the earth again. So, who exactly needs restoration after the flood…?! Chp 55, incidentally, starts with the same imagery I was talking about from RevJohn recently, in the second half of this comment for the “After Death Repentance?” thread. Also, incidentally, I borrowed the blessing of the second half of chp 55, as a blessing from God on Portunista for Book 4 of my series of novels. I have my reasons. 
)
But is the Suffering Servant being punished by God?
Despite translators habitually translating the word “punished” into the text, that word doesn’t really appear in the chapter, except maybe at verse 5. The word there is better translated “chastening”, but of course “chastening” could be construed as “hopeful remedial punishment”, too.
The problem with this interpretation is that it doesn’t best fit the overall context. The preceding verses are set up as an ironic counterpoint: He was despised and rejected by us (v.3), not by God; yet He Himself bore our sicknesses and He carried our pains; and yet we in turn considered Him to be struck down and afflicted by God (v.4). But He was pierced as a result of our transgressions, crushed as a result of our injustices. (v.5)
The prophet’s testimony on the matter is complex. On one hand, yes, God is actively responsible for the suffering of His Servant. And yet somehow we are wrong, ironically so, if we consider the Servant to have been afflicted by God. The poetic logic is summed by verse 6: we all have sinned and gone astray, in other words we all are doers of iniquity; but the Lord has laid our iniquity on His Servant.
The Lord has active responsibility in “crushing Him” (v.10); but His active responsibility in doing so involves ensuring that the Servant suffers as the victim of our injustices; in which self-sacrificial suffering the Servant is also actively complicit, “pouring Himself out to death” (or “submitting Himself to death” as another translation), bearing the sin of many and interceding for the rebels with whom He was reckoned.
This gels very well with chapter 54, where the barren, forsaken widow will no longer remember the shame of her youth but shall be restored by her Husband. Who is her Husband angry at? Not at the Servant! And note the Servant is the one Who died–slain by who? By God, yes, but also by us: this is the “shame of her youth” of the widowed wife–whose Husband is her Makers (the title is plural in Hebrew, incidentally), Whose name is YHWH of Armies, the Holy One of Israel, called the God of all the earth. God doesn’t reject the Servant; God is the Servant (and yet is multiple persons somehow, the Servant and the One Whom the Servant serves). Whom God rejects in wrath is the Bride, who rejected Him and whose adulteries (as poetically described elsewhere, including in Isaiah) the Servant suffers over to His own death: that she (we) might be healed.
“For the Lord has called you, like a wife deserted and wounded in spirit, a wife of one’s youth when she is rejected,” says your God: “I deserted you for a single moment, but I will take you back with great compassion. In a surge of anger I hid My face from you for a moment, but I will have compassion on you with everlasting love,” says YHWH your Redeemer.
Is the chastening of the Servant penal? No; God directs the injustices of us upon Himself–we are the ones who are murdering God, even though God trumps our sin by taking the primary active responsibility for this atrocity. (Which, after all, only makes sense, since we couldn’t do it if He didn’t allow us the ability to. Which is also the point of chp 53.)
Is it substitutionary? I would say not, although there is an ironic counterpoint in the first half of the chapter. The suffering and the responsibility for the suffering is cooperative, not substitutional.
Is it atonement? That is, is it at-one-ment? (Which was the English word originally.) To this I would say yes: God, in actively cooperating with us, in com-passion (passion together), despite our sin, is making at-one-ment with us; and His goal is clearly for us (in poetic conjugal imagery even!) to be at-one-ing with Him again, someday.
“Though the mountains may move and the hills may shake,
My love will not be removed from you,
and My covenant of peace will not be shaken!”
says your compassionate YHWH.
(To the one who has said to herself, in effect: “I am!–and there is none beside me! And I am not a widow!!!”)
